1. Field of the Invention
The present invention relates to the sensing of the rate of rotation of driveshafts and the torque applied thereto.
2. Background Art
For many years, hollow cylindrical drive shafts have been utilized to transmit rotational power between driving and driven components in many different types of vehicles. Drive shafts of this type are typically disposed beneath the bottom of a chassis or frame of the vehicle and, therefore, are exposed to a harsh environment. Frequently, such drive shafts are subjected to relatively large torsional and other stresses of varying magnitudes during normal use. Also, they may be driven at rotational speeds of up to 4000 revolutions per minute during normal use. All of these factors (as well as others) must be accounted for when designing the structure of such a drive shaft, so as to insure that the resulting component will not prematurely fatigue and fail during use. At the same time, it is important not to over-design the drive shaft to have an expected service life which extends long beyond the expected service life of the vehicle itself. Such an over-designed drive shaft would be wasteful in materials and would add undesirable cost and weight to the vehicle.
When designing vehicle drive shafts, reference can be made to techniques which have proven to be effective in evaluating and improving the design of movable mechanical members in general. One of such techniques involves the collection of data related to some of the performance characteristics of the movable member while it is actually in use. Such data acquisition typically entails the sensing of one or more predetermined parameters related to the structure and operation of the movable member. The sensed data is typically collected over a periods of time and stored. When a sufficient amount of data has been sensed and stored, it may be evaluated to generate information related to the sufficiency of the design of the movable member. For example, data acquired in this manner can be useful in determining the life span of the movable member, points of anticipated fatigue or failure on the movable member, the amount of usage of the movable member, and other performance information. Unfortunately, because of the location and nature of use of drive shafts within vehicles, it has not been readily possible to collect real time data related to the operation thereof while the drive shaft is in use on the vehicle. Accordingly, it would be desirable to provide an apparatus and method for gathering such data in this manner.
One such apparatus and method is described in U.S. Pat. No. 4,838,077, issued Jun. 13, 1989, to Shifflet et al, and titled APPARATUS AND METHOD FOR MONITORING THE OPERATION OF A VEHICLE DRIVE SHAFT, assigned to the assignee of the present invention, the disclosure of which patent is incorporated by reference hereinto. Therein, real time data related to certain performance characteristics over a period of time is collected and stored. The data may be subsequently evaluated to generate information regarding such performance characteristics or the sufficiency of the design of the drive shaft. The apparatus comprises an instrument mounted within the hollow shaft and includes a generator having a shaft with a pendulum attached thereto. As the shaft rotates, the pendulum and shaft remain motionless with respect to the rotation of the shaft and the generator provides an analog output proportional to the rate of rotation. The instrument also includes a strain gauge attached to the surface of the shaft which generates an analog output proportional to the torsional stress of the drive shaft. The instrument further includes a temperature sensor which generates an analog output proportional to the ambient temperature therein. The output signals are fed to a a control circuit which provides power to the instrument from batteries disposed within the shaft and which includes a microprocessor and a memory for processing and storing the acquired data. The control circuit also includes a wake-up circuit which generates an electrical output signal to the microprocessor when the drive shaft is rotated. So long as the drive shaft is rotated, the microprocessor maintains the control circuit in an active operating condition, whereby the data is sensed and stored as described above. However, when the drive shaft is not rotated for longer than a predetermined period of time, the microprocessor places the control circuit in a stand-by operating condition, in order to conserve energy consumption.